1. Field of the Invention
The present invention relates to an information recording method and apparatus which carry out a write position control based on a prepit position signal detected during the writing of information to a recording medium, such as a DVD-R, in which prepits, indicative of address information, are formed on the lands between the tracks at given intervals.
2. Description of the Related Art
Recently, write-once or rewritable optical recording media, such as CD-R/RW, and disk drives of such media are put into practical use. These recording media and disk drives are increasingly applied to various kinds of write-once or rewritable applications.
When data is written or rewritten to the optical recording medium of the above type, it is important that an information recording apparatus provides accurate write position control during the writing. If the write position control performed during the writing is inaccurate, there is a possibility that new data to be written to the recording medium and the old data already recorded therein overlap each other. In such a case, the old data or the new data will be destroyed or lost.
In order to provide a write position control, a conventional information recording apparatus uses a linking region placed between an old data area and a new data area of the recording medium. The linking region has a predetermined length. For example, dummy data or control bits are written to the linking region, and then the new data is written to the new data area following the end of the linking region.
According to the conventional method described above, new data cannot be written to the linking regions in the recording medium. Hence, there is a problem in that the storage capacity of the recording medium available for recording information is reduced due to the use of the linking regions. It is desirable to provide an information recording apparatus and method which can carry out accurate write position control during the writing. If accurate write position control is carried out with the information recording apparatus and method, the linking regions where the unnecessary data are recorded can be eliminated or minimized. This will be helpful to increase the storage capacity of the recording medium available for recording information.
As disclosed in Japanese Laid-Open Patent Application No. 9-326138, there is a known apparatus which detects address information and rotation control information of an optical recording medium when recording a signal onto the recording medium. In the recording medium, wobbling grooves, indicative of rotation control information, are formed as the tracks in which information is recorded, and pits, indicative of address information, are formed on the lands between the wobbling grooves at given intervals. The rotation control information is obtained by detecting a wobble signal from the wobbling grooves, and the address information is obtained by detecting a pit signal from the pits. Even when a track pitch of the recording medium is narrow, the information recording apparatus can provide accurate address information and rotation control information, so as to allow high-density recording of the recording medium.
It is possible for the above-mentioned recording apparatus to accurately obtain the address information and the rotation control information from the recording medium even when the track pitch is narrow. However, the address pits indicative of the address information are formed on the lands, not on the tracks (the wobbling grooves) of the recording medium. In other words, the above-mentioned recording apparatus does not place the address information at the start position of one sector along the track of the recording medium. According to the information recording method of this type, the data pits, formed along the tracks, are not interrupted by the address pits, which will provide good compatibility to read-only recording media.
However, if the track pitch of the medium provided by the above-mentioned recording apparatus is narrowed considerably for high-density recording, the influence of crosstalk due to reflection beams from the neighboring grooves of the land radiated by a light beam will not be negligible. When the crosstalk occurs, the wobble signal detected from the recording medium will significantly vary in amplitude or in phase.
In a case in which a write position control is performed with the above-mentioned recording apparatus by using the wobble signal, the occurrence of a phase error of the wobble signal is inevitable, and the above-mentioned recording apparatus is not appropriate for providing accurate write position control.
In the above-mentioned recording apparatus, the address pits indicative of the address information are formed on the lands, not on the tracks of the recording medium. The prepit signal detected from the recording medium is not significantly influenced by the crosstalk and will not vary in amplitude or phase. In a case in which a write position control is performed with the above-mentioned recording apparatus by using the prepit signal, a phase error of the prepit signal is negligible, and the above-mentioned recording apparatus is appropriate for providing accurate write position control.
Generally, however, a laser power of a laser light source used to form a mark (also called a pit) on the recording medium is different from a laser power of the laser light source used to form a space (also called a non-pitted area or a land). It is difficult for the above-mentioned recording apparatus to accurately detect the prepit signal for both the laser powers during the writing to the recording medium, for the purpose of the write position control. The problem of errors in the detection of the prepit position is inevitable, and the above-mentioned recording apparatus is not appropriate for providing accurate write position control.
Further, Japanese Laid-Open Patent Application No. 10-283638 discloses a prepit detection unit of an information recording apparatus. The prepit detection unit disclosed in the above publication is adapted to allow accurate detection of prepits of an optical recording medium by radiating at least two laser beams having different laser powers to the recording medium. The prepit detection unit is directed to eliminating the above-mentioned problem.
The above-mentioned prepit detection unit includes a first prepit detecting circuit that detects a first prepit signal from the recording medium by radiating a first laser beam having a high-intensity laser power used to form a mark, and a second prepit detecting circuit that detects a second prepit signal from the recording medium by radiating a second laser beam having a low-intensity laser power used to form a space. By calculating a logical sum of the detected prepit signals at the first and second prepit detecting circuits, the above prepit detection unit outputs a prepit signal based on the calculated sum.
The above-mentioned prepit detection unit can output the prepit signal for both the first and second laser beams with little prepit position error when the prepit signal is detected from the recording medium during the writing. However, the prepit signal is obtained from the calculated sum of the detection results of the first and second prepit detecting circuits, and it is difficult for the above-mentioned prepit detection unit to obtain a level of accuracy of the detection of the prepit signal that is appropriate for providing accurate detection of the prepit positions for the write position control.
Further, a multipulse recording method which forms a single mark on the recording medium by using a recording waveform having multiple recording pulses is often used for large-quantity information recording. For example, the multipulse recording method is used for the recording of a DVD-R.
However, in the multipulse recording method, the pulse width of the respective recording pulses in the recording waveform is small and the operating state of the laser light source must be frequently changed from ON state to OFF state or vice versa during a short period of time. It is difficult for the multipulse recording method to accurately detect the prepit signal during the writing, for the purpose of the write position control. In the case of the multipulse recording method, the problem of errors in the detection of the prepit positions is inevitable.
Further, in the multipulse recording method, when the prepit signal is detected from the recorded areas of the recording medium, the amplitude of the prepit signal detected is greatly varied because the reflectance of a mark on the medium and the reflectance of a space on the medium are different from each other. With a certain relationship between the prepit position and the mark position, an error in the detected prepit position may take place.
Accordingly, not only when the prepit signal is detected during the writing, but also when the prepit signal is detected from the recorded areas of the recording medium, it is difficult for the conventional information recording methods and devices to obtain a level of accuracy of the detection of the prepit signal that is appropriate for providing accurate detection of the prepit positions for the write position control. In the worst case, the detection of the prepit signal is impossible or errors in the detection of the prepit positions may take place.